Method and system for protecting integrated circuits

Abstract: A high-energy pulse protection device (10) protects an integrated circuit (28 and 30). The integrated circuit (28 and 30) associate with an integrated circuit substrate region (64). The high-energy pulse protection device (10), has a protection circuit substrate region (74) that is disassociated from the integrated circuit substrate region (64). A primary protection circuit (40 and 42) associate with the protection circuit substrate region (74) and has at least one connection (22) with the integrated circuit (28 and 30) for receiving and dissipating through the at least one connection (22) a high-energy pulse. This protects the integrated circuit (28 and 30) from the high-energy pulse.

Description: TECHNICAL FIELD OF THE INVENTION The present invention generally relates to integrated circuits and, more particularly, to a method and system for protecting integrated circuits against a variety of electrical transients. BACKGROUND OF THE INVENTION Integrated circuits are used in a variety of environments including harsh ones that can seriously deter the integrated circuit's proper operation. In general, the phenomena known as electrostatic discharge (ESD) and electrical overstress (EOS) can affect and, in some cases, prohibit the functioning of integrated circuits. ESD may be thought of as high-energy pulse that occurs whenever someone or something carrying an electrical charge touches the integrated circuit. In EOS, a voltage spike of a longer duration exists. An example of EOS occurs when a system is improperly tested or during improper operation of an electrical system that causes a large voltage spike to enter the integrated circuit. In some even harsher environments, such as that of an automobile, a phenomenon known as "load dump" may occur. An example of the load dump electrical transient happens when a battery cable disconnects from the battery terminal as a result of the car hitting a bump or experiencing some other jolt. The disconnected battery cable, if connected to the alternator, may contact a component such as an engine control circuit that has an embedded integrated circuit. This battery cable contact dumps the energy from the alternator into the integrated circuit and can destroy its proper operation. Integrated circuits that protect against ESD often use on-chip protection at the input and output pins. Protection devices that protect against ESD may protect against high-energy pulses of up to 15 kilovolts. On-chip protection device designs for pulses having magnitudes beyond this level are not possible due to practical limits of size on the integrated circuit chip. Circuits that address the EOS and load dump situations may use a metal oxide veristor (MOV) device to absorb the high-energy pulse. MOV devices, however, are bulky and expensive to implement for all integrated circuits that may require protection. The heat that the known protection devices produces also impairs performance of integrated circuits as the temperature rises in the associated silicon substrate region. US-A 4 920 405 discloses an over-current protection circuit for a bipolar transistor. A pair of diodes is connected in series between the base and emitter of the transistor, and a resistor is placed in the emitter lead. When the emitter current through the resistor exceeds a limit value, a current starts to flow through the diodes, and the emitter current is limited. However, the resistor has a positive temperature coefficient of resistance, while the diodes have a negative temperature coefficient, so that heat from the transistor causes the limit value of the emitter current to be reduced. In order to mitigate that effect, the diodes are separated from the semiconductor substrate of the transistor, for thermal isolation. SUMMARY OF THE INVENTION A need, therefore, exists for a method and system that protect integrated circuits against electrical transients such as the ESD, EOS, and load dump transients. A further need exists for a method and system that protect integrated circuits against electrical transients that consume little of the valuable integrated circuit board space and that cost less than know approaches to implement for various types of electrical transients. Yet a further need appears for a method and system that in one embodiment protects integrated circuits against not just one type, but a variety of electrical transients, including ESD, EOS, and load dump situations. That is, the needed method and system should have sufficient flexibility to cover a large range of voltage values that may occur during these transients. The invention provides a high-energy pulse protection apparatus for protecting an integrated circuit as defined in claim 1. Since the protection circuit receives the high-energy pulse protection, instead of the integrated circuit, the integrated circuit is protected against a variety of electrical transients. The trigger circuit triggers upon the high-energy pulse entering the integrated circuit substrate region. This causes the high-energy pulse to flow to the protection circuit. The protection circuit then shunts the high-energy pulse to ground. A technical advantage of the present invention is that it provides a compact, effect, and inexpensive solution to protecting integrated circuits against electrical transients. Because the system of the present invention provides the overvoltage protection circuit on a separate substrate, clamping devices like those of known protection schemes need not consume valuable substrate space of the integrated circuit ship. Another technical advantage of the present invention is that it has sufficient flexibility for use in protecting the integrated circuit against a wide variety of electrical transients, including ESD, EOA, and, in some instances, load dump. Also, the protection circuits formed according to the present invention may take a multitude of designs. For example, a protection circuit may have extremely high voltage and relatively lower voltage spike absorbing portions and connections to the integrated circuit so that only those integrated circuit portions that are likely to experience load dump or EOS connect to the higher voltage absorbing portions. The other integrated circuit components may then connect to the relatively lower voltage spike absorbing portions to protect against ESD. Yet another technical advantage of the present invention is that it removes from the integrated circuit substrate the heat that the protection circuitry generates while protecting the integrated circuit. This insures proper operation of the integrated circuit during and after an electrical transient. A further technical advantage of the present invention is that the protection circuitry on the protection circuitry substrate may include a variety of components for uniform power dissipation such as a semiconductor rectifier (SCR) or a gate-coupled MOSFET (GCM), depending on the type of electrical transients against which the protection circuitry protects. In the case of EOS, the use of large devices with uniform power dissipation can improve reliability and reduce yield loss. The present invention allows the desired sizing of the protection circuit to achieve this. BRIEF DESCRIPTION OF THE DRAWINGS The invention and its modes of use and advantages are best understood by reference to the following Detailed Description of Illustrative Embodiments when read in conjunction with the accompanying drawings, wherein: FIGURE 1 provides a conceptual view of one embodiment of the present invention; FIGURE 2 provides an electrical schematic of one embodiment of the present invention; and FIGURE 3 conceptually illustrates a possible substrate configuration of the FIGURE 2 embodiment. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The illustrative embodiments of the present invention are best understood by referring to the FIGURES wherein like numerals are used like and corresponding parts of the various drawings. In FIGURE 1 appears integrated circuit chip protection package 10 including unprotected integrated circuit chip 12 that protection chip 14 protects. Separating integrated circuit chip 12 from protection chip 14 is thermal isolation layer 16. Integrated circuit chip 12 and protection chip 14 include numerous pins such as pin 18 and pin 20 on the respective chips. Leads 22 connect the pins of integrated circuit chip 12 to those of protection chip 14. Lead 24 illustrates that at least one pin of integrated circuit chip 12 and at least one pin of integrated chip 14 connects to ground. Protection chip 14 contains numerous protection devices that connect individually through associated pins 22 to the integrated circuit components to which associated pins 18 connect. Protection chip 14 and integrated circuit chip 12 use separate substrates. This conserves valuable space on integrated circuit chip 12 and keeps heat that protection chip 14 produces from affecting components on integrated circuit chip 12. Thermal isolation layer 16 separates integrated circuit chip 12 and protection chip 14 substrates, in this example. As an alternative to using simply thermal isolation layer 16, this same concept can be implemented by "piggy-backing" protection chip 14 on top of integrated circuit chip. FIGURE 2 illustrates how integrated circuit chip 12 and protection chip 14 cooperate to provide protection against electrical transients such as those that arising during ESD, EOS, and load dump. Referring to FIGURE 2, dash line 26 depicts the separation between the circuitry on integrated circuit chip 12 and the circuitry of protection chip 14. For example, integrated circuit 12 may include a MOSFET device such as MOSFET device 28 and MOSFET device 30. Connecting to MOSFET devices 28 and 30 are grounded gate MOSFETs 32 and 34. These two devices connect to pins 18 and 19, respectively, through resistors 36 and 38. From pins 18 and 19, leads 22 and 23 connect, respectively, to pins 20 and 21. On protection chip 14, semiconductor rectifier (SCR) 40 connects to pin 20, while SCR 42 connects to pin 21. To trigger SCR 40 on protection chip 14, the ground pins are joined together as indicated by leads 44 and 46 that connect in common at ground pin 48. In FIGURE 2, therefore, grounded gate MOSFETs 32 and 34, respectively, protect MOSFETs 28 and 30 on integrated circuit chip 12 at least to some degree at their input gates. Their additional function is to trigger the primary protection devices of SCRs 40 and 42. As FIGURE 2 illustrates, grounded gate MOSFET 32 and resistor 36 serve as a protector device combination that triggers SCR 40 and causes SCR 40 to turn on. Once triggered, SCRs 40 and 42 protect MOSFETs 28 and 30 to a much higher protection level by shunting the high-energy pulse to ground. Because the ground bus pins for both integrated circuit chip 12 and protection chip 14 are connected in common, the same voltage that goes to grounded gate MOSFET 32 and resistor 36 goes to protection chip 14. For each of the MOSFETs or other integrated circuit components on integrated circuit chip 12, an associated trigger device such as that formed by grounded gate MOSFET 32 and resistor 36 connects to the protected component. Because the primary protection devices, i.e., SCRs 40 and 42 in this example, reside separately on protection chip 14, the space and temperature restrictions that exist on integrated circuit chip 12 do not impose limits on the protection device sizes. Another implementation of the present invention, forms protection chip 14 as part of a multi-chip module (MCM) that includes numerous integrated circuit chips such as integrated circuit chip 12. This embodiment has some or all of the MCM integrated circuit chip connect to the protection chip. Another aspect of the present invention is the flexibility of using different components, instead of or in addition to SCRs, to provide the necessary electrical transient protection. SCRs are attractive because they are highly efficient in triggering and directing electrical transients to ground. Other protection devices may, however, replace the SCR to provide additional or different functions. For example, a MOSFET gate-coupled (GCM) i.e., one having its gate coupled through a resistor to ground to uniformly trigger and dissipate power may be desirable for some EOS applications. These devices are known to result in uniform power dissipation under EOS or ESD. See, e.g. , C. Duvvury, C. Diaz, and T. Haddock, "Achieving Uniform NMOS device power distribution, for Sub-micron ESD Reliability", International Electron Device Meeting 1992, and C. Diaz, S. Kang, and C. Duvvury, "Studies of EOS Susceptibility in 0.6 µm NMOS ESD I/O Protection Structures" EOS/ESD Symposium, September, 1993. A possible disadvantage of using SCRs is the "latch up" problem. In latch-up the SCR turns-on, but fails to turn off even when the voltage falls well below the trigger voltage. In this situation, normal operation of the protected integrated circuit may not resume once the electrical transient ends. To overcome this problem, a GCM may be more attractive. GCM's generally do not have the associated latch-up problem of SCRs. Yet another type of device may be used instead of SCRs 40 and 42 to address the load dump problem. Because of the very high-energy level that the protection circuitry must dissipate in the load dump situation, it is not practical to use a GCM or other MOSFET device. The size limitations required for energy dissipation at the levels occurring during loud dump dictate the use of a large-area SCR or similar device that does not require the amount of area of the MOSFET devices. These and other variations exist fully within the concepts and scope of the present invention. In FIGURE 3 appears a layout of the device connections of the embodiment that appears in FIGURE 2. Referring to FIGURE 3, integrated circuit chip 12 includes lead 52 that may go to other circuitry on integrated circuit chip 12 and that connects to N+ region 54. Lead 56 connects between ground, N+ region 58 and N+ region 54. Connecting also to lead 56 is lead 44 that goes to N+ region 60 of protection chip 14. On integrated circuit chip 12, N- region 62 overlaps N+ region 54 to suppress avalanche at the high end of the resistor 36. The combination of P substrate region 64 with N+ region 54 and N+ region 58 form grounded-gate MOSFET 32. MOSFET 28 is connected to terminal 52 and is not shown in FIGURE 3. On protection chip 14, connections to resistor 36 that lead 22 makes to N+ region 66 and P+ region 68. N- region 70 surrounds N+ region 66 and P+ region 68. N- region 70 overlaps N+ region 72 and together with N+ region 60 form SCR 40 for the necessary triggering and protection of MOSFET 28 on integrated circuit 12. FIGURE 3 also shows ground connection 76 and 78 to P regions 74 and 64 on protection chip 14 and integrated circuit 12, respectively. As an optional connection that the FIGURE 3 embodiment does not require, lead 80 may connect P substrate 74 and P substrate 64 in common to ground. One aspect of the FIGURE 3 embodiment is N+ region 72. U.S. Patent Nos. 5,012,317, A and 4,439,616, A to Robert N. Rountree and assigned to Texas Instruments Incorporated, the assignee hereof (hereinafter such U.S. Patents are called collectively " Rountree ") which are herein incorporated by reference describe use of N+ region 72 to reduce the voltage of the SCR so that it triggers at a lower voltage than what might otherwise be possible. For example, suppose that the designed trigger voltage of SCR 40 is 50 volts. By using N+ region 72 according to the concepts of Rountree it is possible to lower the trigger voltage to 25 volts, for example, so that SCR 40* protects integrated circuit MOSFET 28 at the lower trigger voltage. OPERATION Although the above description sufficiently describes how the various elements of the illustrative embodiments cooperate with one another, the following description of the operation of one embodiment is provided for completeness. FIGURE 2, which illustrates the present embodiment operates to protect against ESD, EOS, and other types of high-energy pulses including some load dump instances. In the FIGURE 2 embodiment, a metal oxide semiconductor device such as MOSFET 32 or 34 breaks down into snapback and the pad voltage built up through resistors 36 and 38, for example, triggers the protection SCR 40 and 42 on protection chip 14. Thus, while gate grounded MOSFETs 32 and 34 together with their respective resistors 36 and 38 dissipate some energy from protected MOSFETs 28 and 30, the main dissipation of energy occurs on protection chip 14. The combination of grounded gate MOSFETs 32 and 36, for example, operates as a trigger device for triggering SCR 40 on protection chip 14. The trigger device that gate grounded MOSFET 32 and resistor 36 form, however, does not provide any hole current into the substrate to trigger SCR, but the SCR triggers only on the conduction through lead 22. In summary, therefore, the present invention provides a high-energy pulse protection apparatus as defined in claim 1. A primary protection device on the protection circuit substrate has at least one connection with the integrated circuit for receiving and dissipating through the connection a high-energy pulse or electrical transient to protect the integrated circuit from the high-energy pulse. This separate substrate for the protection circuit couples with a triggering circuit on the integrated circuit substrate to provide a high degree of circuit protection that is flexible for different levels of energy transients. Although the invention has been described with reference to the above specified embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the above description. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the true scope of the invention.

Claims: A high-energy pulse protection apparatus for protecting an integrated circuit having integrated circuit components (28,30) from an externally created high-energy pulse, the protection apparatus comprising: an integrated circuit (12) located on a first substrate (64) and comprising the said integrated circuit components (28, 30); a primary overvoltage protection circuit (40, 42) located on a second substrate (74) on a separate chip from the first substrate, said second substrate being connected in common with said first substrate (24, 44, 46, 80) to electrical ground, said primary protection circuit having at least one connection (22, 23) with the integrated circuit for receiving a high-energy pulse and dissipating the high-energy pulse through said at least one connection (22, 23) and through said second substrate (74) to said electrical ground (48) for protecting the integrated circuit from the high-energy pulse; and a trigger circuit (32, 34; 36, 38) located on said first substrate (64) and electrically connected to said primary overvoltage protection circuit for triggering said primary overvoltage protection circuit. The protection apparatus of claim 1, wherein said primary overvoltage protection circuit (40, 42) comprises a gate-coupled MOSFET. The protection apparatus of claim 1, wherein said primary overvoltage protection circuit comprises a silicon-controlled rectifier (40, 42). The protection apparatus of any preceding claim, wherein said first and second substrates form part of a multi-chip module (10). The protection apparatus of any preceding claim, wherein the said integrated circuit components protected by the apparatus are MOS transistors (28, 30).

Inventors: DUVVURY CHARVAKA, DUVVURY, CHARVAKA
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1994
Main classification: H01L27
IPC codes: H01L21, H01L25, H01L27